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Topic: Navigation Calculations for Arduino GPS (Read 3 times) previous topic - next topic

kg4wsv

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the altitude is way more accurate than position


Eh?   Altitude is position - the third dimension.

Typical commercial GPS receivers are known to provide poor altitude measurement, especially when the receiver is moving.  The satellites are nearly always low to the horizon, so the errors are a larger percentage of the actual angle being measured.

If you thought you were getting good altitude data, it either wasn't GPS (barometric pressure, etc), the receiver had special firmware, or maybe something was lying to you to make you think the altitude was good.  Or maybe it was the beer.

-j

cyberteque

I was using a topographic map and went to a local trig point, that's government survey data.
But, when I compared barometric altitude, a Freescale MPL115A1, it was pretty close to what the EM-406 read.
To calibrate the MPL115A1, I went over to the Kuitpo AWS, went online, checked the current barometric pressure.
Standing next to the AWS the barometric altitude read the same as the map, as did the EM-406.

I mainly went to that effort because the MPL115A1's temperature reading was and still is, way off.

With my Android tablet, the altitude was spot on, but that uses cell towers to get better data.

Both the Android tablet and EM-406 speed readings are pretty good, I used a straight bit of road and a stopwatch between "mile" posts to check that.


kg4wsv

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Standing next to the AWS the barometric altitude read the same as the map, as did the EM-406.


Standing isn't moving.  A typical GPS does seem to settle down to a decent altitude measurement if you aren't moving, or are moving at a relatively constant speed.

Too bad barometric pressure altitude is weather dependent.  One project in my "when I get time" pile is a rocket tracker that uses an initial GPS measurement to determine MSL and uses that data to adjust baro for a more accurate altitude reading for a rocket tracker.

-j

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